1. Field of the Invention
The present invention relates to an improvement in the structure of a temperature sensitive type fluid fan coupling apparatus for feeding a cooling wind to the engine of an automobile, while controlling the flow rate of the cooling wind of an engine cooling fan automatically by sensing a change in the ambient temperature without interruption in accordance with the running state.
2. Description of the Prior Art
The conventional fan coupling apparatus of this kind is generally constructed, as shown of its essential portion in FIGS. 13 and 14, such that a partition 25 is formed with an outflow adjusting orifice 25' leading from an oil sump 26 to a torque transmission chamber 24 and such that a valve member 28 having its one end fixedly riveted to the partition 25 has its other displaced to and from the outflow adjusting orifice 25' to open or close the outflow adjusting orifice 25' by a connecting rod 29 which is associated with a deformation of a temperature sensing element mounted on the front face of a sealed container in accordance with a change in the ambient temperature.
In this prior art, however, the oil flow rate through the outflow adjusting orifice 25' is controlled by the gap between the valve member 28 and the outflow adjusting orifice 25' of the partition 25. As a result, even if the valve member is precisely associated with the temperature change of the temperature sensing element, this association will not lead to a precise control of the oil flow rate. Specifically, the oil will freely pass through the outflow adjusting orifice 25' till the gap is narrowed to a preset value in the closing stroke of the outflow adjusting orifice 25'. If this gap is reached, the valve member 28 is sucked to the outflow adjusting orifice 25' to narrow the flow passage abruptly by the back pressure of the oil which is pressurized by the centrifugal force from the oil sump 26 to the torque transmission chamber 24. In the opening stroke, on the contrary, the effective passage area is abruptly augmented to increase the inflow of the oil into the torque transmission chamber 24 if the preset gap is reached.
This phenomenon is called the "hunting", which is absolutely contrary to the intrinsic object of the temperature sensitive type fluid fan coupling apparatus for controlling the rotational speed of the fun proportionally of the change in the ambient temperature.
In the prior art having the partition 25 formed with the outflow adjusting orifice 25', moreover, the stroke for opening or closing the outflow adjusting orifice 25' by the valve member 28 is determined by the ratio (i.e., lever ratio) between the distance l.sub.1 between the fixedly riveted portion and the axis of the connecting rod 29 and the distance l.sub.2 between the riveted portion and the outflow adjusting orifice 25'. Since the distance l.sub.2 cannot take a large value, the aforementioned stroke cannot take a large value so that the outflow adjusting orifice 25' can hardly be controlled finely and precisely according to the change in the ambient temperature.
Since, still moreover, the outflow adjusting orifice 25' is so formed inside of the outermost circumference of the oil sump 26 as to avoid the interference between the inner circumference of the oil sump 26 and the aforementioned valve member 28, the oil is fed with many air bubbles from the outflow adjusting orifice 25' to the torque transmission chamber 24. As a result, the torque is transmitted in the aerated state in the gap so that its transmission will fluctuate to make the rotational speed of the fun unstable.